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Hitachi Inverter Problem

A customer had a pump coupling disintegrate recently and the mechanical contractor that fixed it told him that his VFD is hunting and that will shorten the life of though coupler.

I stopped out and checked my loop and its not hunting at all measuring voltage at the DX9100 and at the drive. The drive does however keep saying "Up" and "Down" and the frequency varies by about +/- 0.4Hz. Occasionaly it will say "constant" but not often.

I could just tell the customer that the coupling lasted over 6 years and failure could be caused by minor mis-alignment as the speed varience is very small but I would rather make the VFD stop hunting around. We have not seen this type of drive very often so i'm not sure what to adjust.

Specifics are that its a Model # L-300P-150HBRM / MFG.# 15DFT16642 10049

I'm thinking there is some type of noise my meter can not read on the 0-10vdc input to the drive and I have maxed out parameter A016 which says its and input filter but it did not affect it at all. None of the other setting in the book sound like they would fix this so i'm hoping one of you peoples knows

I am assuming the process variable is a DP device? Maybe filter the input of the DP a bit. You could probably get the PID a bit tighter. You will just have to play with it a while. Double check the drive parameters match the motor nameplate, and adjust DEC, ACC times, ...etc if needed.

Also, on your DX AO verify you are configured for 0-10 in software and the jumpers on the back are set to 0-10 of the DX and not 4-20 ma . or a mixed match. And verify the AI of the drive is set for proper signal the DX is sending out

But the Mechanical Contractor saying this is absurd. Tell him to install the new coupler, get his dial indicator out, do his thing , and then tell him to go away.

If you set the drive to panel control and set the speed, does it still hunt?
The drive might be regulating itself on the current limit.
I am not familiar with Hitachi drives in particular but they all have a limiting function when reaching the programmed current.
If you can, set the motor nominal current a little higher.

Thanks for the replies. No i never tried putting it in manual to see if it still hunts that way. I'll call the customer and see if he can test that today.

I don't think it could be current limited as it normally runs 30-45Hz but has no problems getting to 60Hz as well.

Its not an issue on the DX9100 side as I locked the output to 50%. At the drive i measured 4.98VDC and it never moved yet the speed of the drive kept going from like 29.7Hz to 30.4Hz. Pretty strange. I can't seem to find any type of tech support for these drives but i'll search around a bit more today.